Cadillac DeVille 1985 to 2005 including:1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 1999 DeVille stalling, have codes in Past Cadillac Vehicle Discussion; I just bought this car a few weeks ago, so I don't know much about it. The car is trying ...

1999 DeVille stalling, have codes

I just bought this car a few weeks ago, so I don't know much about it. The car is trying to stall out. The rpm's will drop low then jump back up and keep repeating the same pattern. This mostly happens when at a stop light/sign or even parked. I've started to notice that it does it while driving as well. While this takes place, I'll press on the gas and there seems to be a little bit of hesitation between me pressing the gas and the car responding, which usually ends with the car jolting forward. Even while driiving (under 25mph) and pressing the gas pedal the car seems to drop out as if I let off of the gas pedal. It'll only drop out for a split second but it's long enough to notice the drop.

Just an FYI, I changed the oil and replaced the fuel filter. I do remember the previous owner mentioning replacing the front motor mounts and brakes. I had a few friends make recommendations, like the mass air flow sensor or tune up, etc...

Re: 1999 DeVille stalling, have codes

Do your "friends" even know why you would want to replace the MAF ???? The TB cleaning is the first place to start - then make sure the 4 coils are clean and that their base contacts are clean - and that the ICM ground cable terminals are clean and tightly connected.

Fuel filters are almost never a problem.

Spark plug cable connection diagram in my albums. Study the entire Cadillac Technical Archive way up ^^^ in the black bar, then read all the sticky posts just above this one as well as Discussions, Cadillac Tech Tips and the stickys at the top of Engines, Northstar Performance.

Re: 1999 DeVille stalling, have codes

Originally Posted by MoistCabbage

How many miles on the car?

When was the last time the TB was cleaned.

Car has 145k. I dont know when the tb was cleaned.

Originally Posted by Submariner409

Do your "friends" even know why you would want to replace the MAF ???? The TB cleaning is the first place to start - then make sure the 4 coils are clean and that their base contacts are clean - and that the ICM ground cable terminals are clean and tightly connected.

Fuel filters are almost never a problem.

Spark plug cable connection diagram in my albums. Study the entire Cadillac Technical Archive way up ^^^ in the black bar, then read all the sticky posts just above this one as well as Discussions, Cadillac Tech Tips and the stickys at the top of Engines, Northstar Performance.

I appreciate everyone's response. You all recommended some good avenues to go down. I'll try each one and see where it leaves me. I'll post up when (IF) the issue is fixed. Thanks again.

Re: 1999 DeVille stalling, have codes

Where would I check for a vacuum leak? Thanks

Can anyone tell me the difference between the ac delco 41-950 and the 41-987? I found the 41-950 on the rockauto website for $4.58 plus (I think) $1.50 mail-in rebate for each plug which brings them to $3.08. I couldn't find the 41-987 plugs on the rockauto site. Also, can someone tell me the difference between the different sets of ac delco spark plug wires? Is there anything else I should pick up from rockauto?

Re: 1999 DeVille stalling, have codes

Check all the vacuum lines and connections, manifold mounting, over pressurization relief valve.

Not sure what the exact difference is between the 950 & the 987, but 900 series is double platinum. 41-950 are for the pre-2000 engines and the 41-987's are for the 2000+'s. I suspect maybe a different heat range since the 2000+ had the compression ratio very slightly reduced.

The difference in the plug wires is that the more expensive set (748J) are custom fit for length.

Re: 1999 DeVille stalling, have codes

Hey fellas, I did the tune up. Unfortunately it's still stalling on me. It actually shut off on me just yesterday. In an effort to troubleshoot, ill be cleaning the throttle body, checking over the vacuum lines and while I'm at it I'm going to replace the water pump belt tensioner and valve cover gasket. I'm going to look through some old post to see if I can find something helpful but if you know of any specific threads that actually cover the work I plan on doing, please post it up. If you can think of anything else I need to do or check while I'm at it, I'd appreciate the heads up.

Re: 1999 DeVille stalling, have codes

Have fun changing the cam cover seals. Many hoops to jump through, including PROPERLY removing the water pump drive pulley from the left bank intake cam extension .......... and proper replacement. Do it wrong and you're in the big bucks repair business. How about the spark plug well cam cover seals ???

Use the 41-950 plugs, damn any cost differences. 13 lb/ft of torque, a tad of anti-seize on the 1st 3 plug threads. New AC Delco wires, too. Proper connection diagrams in my albums. (Yes, each coil has a proper connection pattern)(The reason you couldn't find the 41-987 plugs in your car listings is because they aren't recommended for your engine)

Re: 1999 DeVille stalling, have codes

It seems to be getting worse. Every time I drive its a gamble on wether ill make it home. It looks like every time it gets to operating temperature the rpm's drop and rise. If I let it go on too long with out pushing on the gas, the car will stall out. While this takes place you can smell gas. I took it to a chevy dealer and they told me it was one of these problems

A friend told me that the blow back valve is the Pcv. I went to auto zone and was told that the northstar engines come with two pcv's (one in front near engine oil cap and one in the rear). I replaced the one in the rear. No noticeable difference so I then had the dealer replace the intake manifold gasket. Again, no noticeable difference. My most recent and last effort was getting the exhaust leak sealed up. These things might've needed to be replaced but didn't fix the main issue. I don't think that a carbonized throttle plate can cause this issue so I'm assuming its the fuel pump. Any thoughts?

Re: 1999 DeVille stalling, have codes

At least two of your info sources are wrong - the "blowback" valve (the intake manifold overpressure valve) is in the passenger end of your year intake manifold. It prevents manifold breakage in the event of a backfire. It could have been cleaned or replaced when the intake was off - by a tech that knew what he/she was doing.

Your car has one PCV valve - the one in the right (rear) cam cover. The other pipe - left (front) cam cover is the fresh air intake from the atmospheric side of the throttle butterfly.

A dirty throttlebody and idle air passage can cause stalling. All posted in these forums a million times.

Most of your posted list of faults is discussed in Discussions - Cadillac Tech Tips.

I have been dealing with a similar issue on my 2001 sts. The other day I used some carb cleaner and started spraying vacum lines with the car running. I was about 2 minutes into it when I sprayed the rubber plenum gasket between the intake and manifold. It turns out this is a well documented problem on the north star engine. I was able to order the part from ohriley auto with the manifold gasket for 30 dollars. Car is getting much better gas mileage and runs perfectly. Please let me know how it goes.